The present invention generally relates to self-expanding endoprosthesis devices, in particular self-expanding intraluminal vascular grafts, generally called stents, adapted to be implanted in a body lumen, such as carotid arteries, coronary arteries, peripheral arteries, veins, or other vessels to maintain the patency of the lumen. These devices are frequently used in the treatment of atherosclerotic stenosis in blood vessels especially after percutaneous transluminal angioplasty (PTA) or percutaneous transluminal coronary angioplasty (PTCA) procedures, with the intent to reduce the likelihood of restenosis of a vessel. Stents are also used to support a body lumen, tack-up a flap or dissection in a vessel, or in general where the lumen is weak to add support. The present invention also relates to an intraluminal vascular graft that can be used in essentially any body lumen.
In expandable stents that are delivered with expandable catheters, such as balloon catheters, the stents are positioned over the balloon portion of the catheter and are expanded from a reduced diameter to an enlarged diameter greater than or equal to the inner diameter of the arterial wall, by inflating the balloon. Stents of this type can be expanded to an enlarged diameter by deforming the stent, by engagement of the stent walls with respect to one another, and by one way engagement of the stent walls together with endothelial growth onto and over the stent. Other stents are self-expanding, through the properties of the material constituting the stent or by design. Examples of intravascular stents can be found in U.S. Pat. No. 5,292,331 (Boneau); U.S. Pat. No. 4,580,568 (Gianturco); U.S. Pat. No. 4,856,516 (Hillstead); U.S. Pat. No. 5,092,877 (Pinchuk); and U.S. Pat. No. 5,514,154 (Lau et al.), which are incorporated herein by reference in their entirety.
The problems with some prior art stents, especially those of the expandable type, is that they are often stiff and inflexible. Often, the expandable type stents are formed from stainless steel alloys and the stents are constructed so that they are expanded beyond their elastic limit. Such stents are permanently deformed beyond their elastic limits and are capable of holding open a body lumen and maintaining patency of the body lumen. There are several commercially available stents that are widely used and generally implanted in the coronary arteries after a PTCA procedure.
Stents also are implanted in vessels that are closer to the surface of the body, such as in the carotid arteries in the neck or in peripheral arteries and veins in the leg. Because these stents are so close to the surface of the body they are particularly vulnerable to impact forces that can partially or completely collapse the stent and thereby block fluid flow in the vessel. Since the prior art stents are plastically deformed, once collapsed or crushed they will remain so, permanently blocking the vessel. Thus, the prior art stents can pose an undesirable condition to the patient.
Other forces can impact the prior art stents and cause similar partial or total vessel blockage. Under certain conditions, muscle contractions might cause the prior art stents to partially or totally collapse and restrict blood flow in the vessel in which they are implanted.
Attempts have been made to make stents out of shape memory alloys (see discussion infra), but dislodgment from the implant site may result if these prior art stents are temporarily crushed due to external forces.
What has been needed and heretofore unavailable in the prior art stents is a stent that is formed from a metal alloy having crush-resistant and recovery properties and, importantly, that will not dislodge from the implant site if it is temporarily crushed due to external forces. The present invention satisfies these needs.